Light guiding inside a liquid-jet, also of laser light with an energy level below a material damage threshold, is a well-known effect, and does not require a precise alignment of the light into the liquid-jet.
To perform material treatment of a work piece using a liquid-jet guided laser beam, the laser power however must exceed the damage threshold of the work piece material. In such case exact focus alignment of the laser beam into the liquid-jet, as well as hydrodynamic effects of the liquid-jet play a very important role and must be considered accurately.
For exploitation of the technology in industrial environments that require manless 3-shift operation it is extremely important that the liquid-jet laser process is able to operate stable for a long uninterrupted time while applying a high laser power for treatment of the work piece.
Without the right focus alignment, the energy level of a laser in many is so high, that the nozzle, which creates the liquid-jet, and/or the protection window, which closes the liquid stagnation space and thru which the laser is focused into the liquid-jet, will be destroyed either immediately or after a very short number of working hours; hence the right kind of optical focus alignment as well as hydrodynamic considerations must be followed.
Thus there is a need for methods that allow reliable coupling of a high-power laser beam into a liquid-jet while significantly increasing the lifetime of the nozzle and the protection window.